Few novelists write about madness as well as Donald Antrim. Not necessarily full-blown, off-the-wall psychopathic insanity - though he does that too - but the slow-motion slippage into craziness; the casual sliding in and out of competing versions of reality; the tolerable and tolerated regions of personal eccentricity that border and subtly encroach on the territory we like to call normality.

Antrim's three previous books are intrepid, darkly hilarious novels that venture into these different sorts of madness. All three centre on young or young-ish male narrators who, in a variety of gloriously surreal settings, hurtle towards psychological and physical meltdown. The Verificationist , for instance, is set in a downtown pancake house where Tom and 19 psychoanalyst colleagues are having their biannual get-together. Twenty pages in, Tom has an out-of-body experience that transports him to the ceiling of the restaurant, where he remains, narrating tirelessly, for the rest of the book.

Antrim's novels are subversive, anarchic, digressive, provocative, comically outrageous. Think Virginia Woolf stoned, Faulkner on acid, Nabokov on speed. In The Afterlife , Antrim gives us something altogether more grounded, and for that reason all the more disturbing: a "true" account of his childhood and, in particular, his anguished relationship with his mother, Louanne Antrim, a woman whose life is one long tale of sound and fury, and whose bequest to her son is the task of working out what, if anything at all, it signifies. "Conflict is the really interesting thing, I've found," reflects the central character in Antrim's The Hundred Brothers. "Conflict! Conflict is always so difficult to recount. By difficult I mean painful. But also I mean demanding. The technical aspects of describing true conflict are daunting. First you have to establish your antagonists ... The problems in describing a person are essentially problems of knowing a person."

Knowing Louanne Antrim was made more difficult by her alcoholism, paranoia and hysteria. She believed she'd been a Roman galley slave in a former life and had drowned, shackled to the oars. She was convinced her pulmonary specialist wanted to have sex with her. Her cat was an incarnation, she claimed, of Merlin. She made beautifully tailored, unwearable garments, combed her hair so it looked uncombed. Bourbon-fuelled fights between Antrim's parents were commonplace. She had screaming fits that went on all night. "Her power to drive people away was staggering," Antrim drily observes.

Louanne, who married, divorced, remarried and redivorced the same man, emerges as a woman determined to a near-heroic degree to confront herself, yet chronically unable to do so. Instead - like many mothers before and since - she indulged a brutal capacity to manipulate her son's loyalty and affection in the service of her own needy egotism. (Her maiden name, appropriately enough, was Self.) He was to be her confidant, her true husband; his impossible and defining task was "to be both like and unlike all other men". This, Antrim believes, was the cause of the debilitating asthma from which he suffered as a child. "I was a boy dying for his mother, angrily, stubbornly doing her work of dying, the work she had begun before I was born ... I was not merely bringing my mother to my bedside, not simply bringing her close. Rather, I was marrying myself to her, learning to speak the language of her unconscious, which, as time would bear out, was a language of suffocation and death."

Antrim is too intelligent a writer to lay all the blame for his mother's ruined life at her feet alone. As the book's subtitle quietly points out, this is a tale of "relative insanity" - and what relatives! There is Uncle Eldridge, who dies a recluse with a car boot full of high-calibre handguns and unopened cases of ammunition. There is Roxanne, Louanne's mother, the health obsessive who "used health to suppress everyone around her" and subjected her only daughter to countless needless operations. There is the shadowy figure of Antrim's father, the literature professor who refused to discuss books with his bookish son.

In the months after Louanne's death, Antrim embarks on a quest for the perfect bed. He spends hours in department stores trying them out. He becomes an expert in beds and bed-makers. Shifman, Sealy, Stearns & Foster. He buys one, sends it back, buys another, cancels the order before delivery. Months go by in pursuit of perfection. Eventually he settles for a Dux, the creme de la creme, $7,000-worth of bed. It is, unsurprisingly, a disaster: "I sank into the bed and tried to want it. And the further I sank into it the closer I came to knowing what the bed was. It was the last bed I would ever buy. It was the bed that would deliver me into my fate. It was the bed that would marry me again to my mother, the bed Louanne and I would share ... The bed was alive with my mother. I sank into the bed, and it was as if I were sinking down into her arms. "She was not beside me on the bed, she was inside the bed, and I was inside the bed; and she was pulling me down into the bed to die with her. "It was my deathbed. It was a coffin. It was a sarcophagus. I didn't want to die. Did I?"

The Afterlife bears many similarities to the novels that precede it. Here, too, the story is told by a first-person male narrator and involves frequent digressions into apparently unrelated subjects, drawn-out meanderings through off-kilter interior alleyways. Reality and its chief protector, truth, are at best precarious. All four books are in a sense volumes of the same work: a portrait of the artist, viewed from different angles. In The Afterlife , however, the dazzling surrealist antics of Antrim's novels are transposed into a more sombre key of realism. The result is a powerful, tender, entirely compelling portrait of familial dysfunction and its long, painful legacy.